Great interest and resources have been directed towards developing technologies that use renewable energy or waste energy or low cost syngas or producer gas for the production of useful organic chemicals, which provide alternatives to chemicals, materials and fuels derived from petroleum or other fossil sources; as well as chemicals, materials and fuels derived from purpose grown crops that compete with food production or negatively impact natural habitats. These alternative approaches to the sustainable production of organic chemicals can involve the conversion of carbon dioxide, or other relatively low value carbon sources such as but not limited to lignocellulosic energy crops, crop residues, bagasse, saw dust, forestry residue, food waste, municipal solid waste, sewage, waste carpet, biogas, landfill gas, stranded natural gas, or pet coke. The conversion of low value fixed carbon sources such as but not limited to lignocellulosic energy crops, crop residues, bagasse, saw dust, forestry residue, food waste, municipal solid waste, sewage, waste carpet, biogas, landfill gas, stranded natural gas, or pet coke, to organic chemicals, often involves a syngas or producer gas intermediate—a stream of gas that is rich in hydrogen and/or carbon monoxide, which can be generated from the said fixed-carbon source using gasifier, partial oxidation, steam reforming, or pyrolysis technologies known in the art. Most of the focus in the area of CO2 conversion has been placed on biological approaches that utilize photosynthesis to fix CO2 into biomass or organic end products, while some effort has been directed at fully abiotic and chemical processes for fixing CO2.
A type of CO2-to-organic chemical approach that has received relatively less attention is hybrid chemical/biological processes where the biological step is limited to the fixation of C1 compounds, such as CO2, alone, which corresponds to the dark reaction of photosynthesis, while reducing equivalents needed for carbon-fixation are generated through an abiotic process, thus substituting for the light reaction of photosynthesis. The potential advantages of such a hybrid CO2-to-organic chemical process include the ability to combine enzymatic capabilities gained through billions of years of evolution in fixing C1 compounds such as CO2, with a wide array of abiotic technologies to power the process such as solar PV, solar thermal, wind, geothermal, hydroelectric, or nuclear, which can be used to generate reducing equivalents needed for carbon fixation, and particularly hydrogen gas or reduced hydrogen atoms or hydride, with established electrolysis technologies from abundant water resources, and particularly non-potable water, salt water, and brine sources. Another potential advantage is the possibility of using syngas or producer gas that is primarily comprised of C1 compounds and hydrogen gas, which represents a low cost carbon source and source of reducing equivalents since it can be readily generated from an array of low cost or waste feedstocks such as lignocellulosic energy crops, crop residues, bagasse, saw dust, forestry residue, food waste, municipal solid waste, sewage, waste carpet, biogas, landfill gas, stranded natural gas, or pet coke, using readily available gasifier, partial oxidation, steam reforming, or pyrolysis technologies known in the art. Microorganisms performing carbon fixation without light can generally be contained in more controlled and protected environments, less prone to water and nutrient loss, contamination, or weather damage, than what can be used for culturing photosynthetic microorganisms such as algae or cyanobacteria. Furthermore an increase in bioreactor capacity can be readily met with vertical rather than horizontal construction, making it potentially far more land efficient than photosynthetic approaches. A hybrid chemical/biological system offers the possibility of a C1-to-organic chemical process that avoids many drawbacks of photosynthesis while retaining the biological capabilities for complex organic synthesis from CO2 and other C1 molecules.
Chemoautotrophic microorganisms are generally microbes that can perform CO2 fixation like in the photosynthetic dark reaction, but which can get the reducing equivalents needed for CO2 fixation from an inorganic external source, rather than having to internally generate them through the photosynthetic light reaction. Carbon fixing biochemical pathways that occur in chemoautotrophs include the reductive tricarboxylic acid cycle, the Calvin-Benson-Bassham cycle, and the Wood-Ljungdahl pathway.
Prior work is known relating to certain applications of chemoautotrophic microorganisms in the capture and conversion of CO2 gas to fixed carbon as well as in the biological conversion of syngas or producer gas to fixed-carbon products. However, many of these approaches have suffered shortcomings that have limited the effectiveness, economic feasibility, practicality and commercial adoption of the described processes. The present invention in certain aspects addresses one or more of the aforementioned shortcomings.